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At least 991 records · Page 55Linked to original sources
PubMed2003

Life-history differentiation and the maintenance of monoecy and dioecy in Sagittaria latifolia (Alismataceae).

The existence of monoecious and dioecious populations within plant species is rare. This limits opportunities to investigate the ecological mechanisms responsible for the evolution and maintenance of these contrasting sexual systems. In Sagittaria latifolia, an aquatic flowering plant, monoecious and dioecious populations exist in close geographic proximity but occupy distinct wetland habitats differing in the relative importance of disturbance and competition, respectively. Life-history theory predicts contrasting evolutionary responses to these environmental conditions. We propose that the maintenance of monoecy and dioecy in S. latifolia is governed by ecological selection of divergent life-history strategies in contrasting habitats. Here we evaluate this hypothesis by comparing components of growth and reproduction between monoecious and dioecious populations under four conditions: natural populations, a uniform glasshouse environment, a common garden in which monoecious and dioecious populations and their F1 progeny were compared, and a transplant experiment using shaded and unshaded plots in a freshwater marsh. Plants from dioecious populations were larger in size and produced heavier corms in comparison with monoecious populations. Monoecious populations flowered earlier and produced more flowers, clonal ramets, and corms than dioecious populations. The life-history differences between the sexual systems were shown to have a quantitative genetic basis, with F1 progeny generally exhibiting intermediate trait values. Survival was highest for each sexual system in field plots that most closely resembled the habitats in which monoecious (unshaded) and dioecious (shaded) populations grow. These results demonstrate that monoecious and dioecious populations exhibit contrasting patterns of investment in traits involved with growth and reproduction. Selection for divergent life histories between monoecious and dioecious populations of S. latifolia appears to be the principal mechanism maintaining the integrity of the two sexual systems in areas of geographic overlap.

Adaptation, Physiological↗
PubMed2004

Maternal effects influence the sexual behavior of sons and daughters in the zebra finch.

Individual differences in sexual behavior have received much attention by evolutionary biologists, but relatively little is known about the proximate causes of this variation. We studied the quantitative genetics of male and female sexual behavior of captive zebra finches and found surprisingly strong maternal effects (differing between individual mothers) on the aggressiveness and song rate of sons and on the daughters' mating preferences for these male traits. We also found that daughters differed in their choosiness during mate-choice experiments depending on whether they originated from eggs produced early or late within the laying sequence of a clutch. Because this effect of laying order occurred independently of hatching order in cross-fostered broods, it must have been caused by consistent within-mother variation in maternal effects transmitted through the egg. Our findings raise the question whether these maternal effects might represent strategic programming of offspring behavior in response to the environment experienced by mothers or whether they are merely nonadaptive byproducts of developmental processes.

Aggression↗
PubMed2004

Social polyandry, parental investment, sexual selection, and evolution of reduced female gamete size.

Sexual selection in the form of sperm competition is a major explanation for small size of male gametes. Can sexual selection in polyandrous species with reversed sex roles also lead to reduced female gamete size? Comparative studies show that egg size in birds tends to decrease as a lineage evolves social polyandry. Here, a quantitative genetic model predicts that female scrambles over mates lead to evolution of reduced female gamete size. Increased female mating success drives the evolution of smaller eggs, which take less time to produce, until balanced by lowered offspring survival. Mean egg size is usually reduced and polyandry increased by increasing sex ratio (male bias) and maximum possible number of mates. Polyandry also increases with the asynchrony (variance) in female breeding start. Opportunity for sexual selection increases with the maximum number of mates but decreases with increasing sex ratio. It is well known that parental investment can affect sexual selection. The model suggests that the influence is mutual: owing to a coevolutionary feedback loop, sexual selection in females also shapes initial parental investment by reducing egg size. Feedback between sexual selection and parental investment may be common.

Animals↗
PubMed1987

Restriction fragment length polymorphisms in dairy and beef cattle at the growth hormone and prolactin loci.

Two bovine populations, a Holstein-Friesian dairy stock and a synthetic (Baladi X Hereford X Simmental X Charolais) beef stock, were screened for restriction fragment length polymorphisms (RFLPs) at the growth hormone and prolactin genes. Most RFLPs at the growth hormone gene are apparently the consequence of an insertion/deletion event which was localized to a region downstream of the structural gene. The restriction map for the genomic region including the growth hormone gene was extended. Two HindIII RFLPs at the growth hormone locus, as well as several RFLPs at the prolactin gene, seemed to be the consequence of a series of point mutations. The results are discussed in terms of the possibility that minor genomic variability underlies quantitative genetic variation.

Animals↗
PubMed2004

Constrained sex allocation in a parasitoid due to variation in male quality.

The theory of constrained sex allocation posits that when a fraction of females in a haplodiploid population go unmated and thus produce only male offspring, mated females will evolve to lay a female-biased sex ratio. I examined evidence for constrained sex ratio evolution in the parasitic hymenopteran Uscana semifumipennis. Mated females in the laboratory produced more female-biased sex ratios than the sex ratio of adults hatching from field-collected eggs, consistent with constrained sex allocation theory. However, the male with whom a female mated affected her offspring sex ratio, even when sperm was successfully transferred, suggesting that constrained sex ratios can occur even in populations where all females succeed in mating. A positive relationship between sex ratio and fecundity indicates that females may become sperm-limited. Variation among males occurred even at low fecundity, however, suggesting that other factors may also be involved. Further, a quantitative genetic experiment found significant additive genetic variance in the population for the sex ratio of offspring produced by females. This has only rarely been demonstrated in a natural population of parasitoids, but is a necessary condition for sex ratio evolution. Finally, matings with larger males produced more female-biased offspring sex-ratios, suggesting positive selection on male size. Because the great majority of parasitic hymenoptera are monandrous, the finding of natural variation among males in their capacity to fertilize offspring, even after mating successfully, suggests that females may often be constrained in the sex allocation by inadequate number or quality of sperm transferred.

Analysis of Variance↗
PubMed2006

Strong environmental determination of a carotenoid-based plumage trait is not mediated by carotenoid availability.

Carotenoid-based colours are recognized as having an important signalling function, yet the nature of the mechanisms that maintain their honesty is not well understood. By combining a carotenoid-feeding experiment with a quantitative genetic experiment in a wild population of blue tits (Parus caeruleus), we were able to test predictions that differentiate between proposed mechanisms. If variation in carotenoid ingestion underlies variation in carotenoid-based colour expression, then carotenoid-supplemented birds should have reduced variance in colour. In this study, carotenoid supplementation produced a small but significant change in plumage colouration, but no significant change in variation. These results suggest that variation in carotenoid acquisition is not an important source of variation for this colour trait, and that variation in post-ingestion processes are likely to be more important. The low heritability of this colour trait suggests environmental factors are likely to underlie the majority of variation in these processes.

Animals↗
PubMed2006

Ecosystem engineers as selective agents: the effects of leaf litter on emergence time and early growth in Impatiens capensis.

By physically modifying the abiotic environment, ecosystem engineers can have dramatic effects on the distribution and abundance of species in a community. However, ecosystem engineering can also change the selective environment and evolutionary dynamics of affected species, although this remains relatively understudied. Here, we examine the potential for an ecosystem engineer - oak trees - to affect the evolutionary dynamics of the herbaceous, understory annual, Impatiens capensis, through leaf litter deposition. Using a quantitative genetic experimental approach, we found that: (i) the presence of leaf litter significantly affected a suite of germination, growth and phenological traits in I. capensis; (ii) I. capensis does not exhibit performance trade-offs across litter and bare soil environments in the form of negative across-environment genetic correlations; (iii) the presence or absence of leaf litter significantly alters the pattern of natural selection germination timing and hypocotyl length; and (iv) the frequency of leaf litter environments can dramatically change which combinations of hypocotyl length lead to highest mean fitness across both bare soil and leaf litter environments. More generally, our results demonstrate the potential for ecosystem engineers to alter both the ecological and the evolutionary dynamics of the species they affect.

Ecosystem↗
PubMed2005

Phenotypic impacts of repetitive DNA in flowering plants.

The discovery that nuclear DNA content varies widely among species, and even within species, was unexpected because it was thought that the number of genes required for an organism should be common across taxa. We now know that the bulk of nuclear DNA content variation is caused by repetitive DNA sequences characterized according to the nature of repeat (tandem vs dispersed) or chromosomal location/mechanism of replication (pericentromeric, telomeric or subtelomeric, microsatellites, minisatellites, satellites, transposable elements, retroelements). Variation in repetitive DNA, manifested as variation in nuclear DNA content, has been shown to have broad ecological and life-history consequences. For example, large genome size appears to limit fitness in extreme environmental conditions. Within species, variation in DNA content has been coupled to growth and development, such as maturation time in crop species. In Silene latifolia, DNA content is negatively correlated with flower size, a character that, in turn, has well documented ecological significance. These intraspecific studies suggest a connection between repetitive DNA and quantitative genetic determination of continuous characters. Novel insights into mechanisms by which repetitive DNA influences phenotype will lead to models of evolutionary change that extend well beyond the conventional view of evolution by allelic substitution.

DNA, Plant↗
PubMedDate not supplied

The effect of development on the direction of evolution: toward a twenty-first century consensus.

One of the most important questions in evolutionary biology is: what orients the evolutionary process? That is, what causes evolution to proceed toward certain developmental trajectories, and hence phenotypes, rather than others? In particular, there has been prolonged controversy over whether the direction of evolution is determined solely by external factors or whether the nature of the ontogenetic process, and the ways in which it can be altered by mutations in developmental genes, may also play a major role. Here, I examine this issue, concentrating on the following: the possible evolutionary orienting role of "developmental bias;" the question of whether selection can and/or will break bias; the extent to which bias is already incorporated in quantitative genetic studies; and ways of approaching the possible role of bias in the origin of evolutionary novelties. Finally, I suggest that developmental bias may provide a focal point for the coming together of conceptual and practical approaches to evo-devo.

Biological Evolution↗
PubMed2026

Predictive evolutionary genomics: principles, validation, and practice.

Climate change and habitat loss are driving rapid evolutionary responses in populations world-wide, which creates an urgent need for evolutionary forecasting in conservation and agriculture. Such forecasting can be categorized into three time scales: trait-based models that use multivariate quantitative genetic equations to project correlated phenotypic responses up to c. 20 generations, allele-based analyses that model allele frequency dynamics up to 100 generations, and composite adaptation scores that aggregate many small effects to yield predictions across longer horizons. However, these approaches have remained largely disconnected. Here, we present a Bayesian framework that integrates these three complementary approaches for evolutionary prediction. Our framework combines genomic, phenotypic, and environmental data to yield probabilistic predictions with explicit uncertainty. We show how predictive evolutionary forecasts can be validated with experimental evolution, field experimentation, historical specimens, and reciprocal transplants. These validated forecasts can help advance conservation and agricultural programmes by helping predict which populations are at risk of future extinction, optimizing breeding programmes for future climates, and planning ecosystem management under environmental change. By supporting a shift towards more predictive approaches in evolutionary biology, this framework may help improve our ability to manage biodiversity and food security in a changing world.

Genomics↗
PubMed1989

The mysteries of lipoprotein(a).

Lipoprotein(a) [Lp(a)] is a macromolecular complex found in human plasma that combines structural elements from the lipoprotein and blood clotting systems and that is associated with premature coronary heart disease and stroke. It is assembled from low-density lipoprotein (LDL) and a large hydrophilic glycoprotein called apolipoprotein(a) [apo(a)], which is homologous to the protease zymogen plasminogen. Plasma Lp(a) concentrations vary 1000-fold between individuals and represent a continuous quantitative genetic trait with a skewed distribution in Caucasian populations. Variation in the hypervariable apo(a) gene on chromosome 6q2.6-q2.7 and interaction of apo(a) alleles with defective LDL-receptor genes explain a large fraction of the variability of plasma Lp(a) concentrations. Though of high theoretical and practical interest, many aspects of the metabolism, function, evolution, and regulation of plasma concentrations of Lp(a) are presently unknown, controversial, or mysterious.

Arteriosclerosis↗
PubMed1996

Longevity, genes, and aging.

Until recently, biogerontology was a backwater of biology, but progress in the qualitative and quantitative genetic analysis of longevity has led to a revolution in aging research. This research has revealed that extended longevity is frequently associated with enhanced metabolic capacity and response to stress. Moreover, it suggests that there are multiple mechanisms of aging. Because of its complexity, the aging process takes us into the realm of integrative biology, and thus, biogerontology should prove instrumental in deciphering the functional and regulatory circuitry of the sequenced genome.

Aging↗
PubMed1997

Instability of CAG and CTG trinucleotide repeats in Saccharomyces cerevisiae.

A quantitative genetic assay was developed to monitor alterations in tract lengths of trinucleotide repeat sequences in Saccharomyces cerevisiae. Insertion of (CAG)50 or (CTG)50 repeats into a promoter that drives expression of the reporter gene ADE8 results in loss of expression and white colony color. Contractions within the trinucleotide sequences to repeat lengths of 8 to 38 restore functional expression of the reporter, leading to red colony color. Reporter constructs including (CAG)50 or (CTG)50 repeat sequences were integrated into the yeast genome, and the rate of red colony formation was measured. Both orientations yielded high rates of instability (4 x 10(-4) to 18 x 10(-4) per cell generation). Instability depended on repeat sequences, as a control harboring a randomized (C,A,G)50 sequence was at least 100-fold more stable. PCR analysis of the trinucleotide repeat region indicated an excellent correlation between change in color phenotype and reduction in length of the repeat tracts. No preferential product sizes were observed. Strains containing disruptions of the mismatch repair gene MSH2, MSH3, or PMS1 or the recombination gene RAD52 showed little or no difference in rates of instability or distributions of products, suggesting that neither mismatch repair nor recombination plays an important role in large contractions of trinucleotide repeats in yeast.

DNA Repair↗
PubMed1978

Inducibility of aryl hydrocarbon hydroxylase in cultured human lymphocytes: a study of repeatability.

Modifications to the method for estimating aryl hydrocarbon hydroxylase (AHH) activity in cultured human lymphocytes are described. Despite the improvements to the technique it was not possible to show significant 'repeatability' of values for AHH induction over a period of 2 weeks or more. Significant repeatability could be seen when a blood sample from each subject was split into duplicates. However, this level of repeatability was low when considered for quantitative genetics purposes. Possible reasons for the poor repeatability have been discussed.

Adult↗
PubMed2002

Gene-environment interplay in relation to emotional and behavioral disturbance.

The conceptual and methodological issues involved in the study of gene-environment correlations (rGE) and interactions (GxE) are discussed in historical context. Quantitative genetic findings are considered with respect to rGE and GxE in relation to emotional and behavioral disturbance. Key conceptual and substantive implications are outlined in relation to both genetic and environmental risk mediation, with a brief note on evolutionary considerations.

Affect↗
PubMed1996

Triiodothyronine exerts a major pleiotropic effect on reverse cholesterol transport phenotypes.

The thyroid hormone triiodothyronine (T3) is known to be a potent mediator of APOA1 gene expression. With the use of multivariate quantitative genetic analysis, we have assessed the magnitude of shared effects of T3 on plasma concentrations of apolipoprotein AI (apo AI) and three related phenotypes: HDL-C, apo AII, and LpAI (which is a concentration of apo AI that contains HDL particles). Maximum likelihood techniques were used to simultaneously estimate mean effects and variance components in large, extended Mexican American families living in San Antonio, Tex. We found that T3 accounted for 16%, 23%, 21%, and 37% of the additive genetic variance in HDL-C, apo AI, apo AII, and LpAI, respectively, while explaining virtually none of the random environmental variance in these phenotypes. T3 also has a pronounced effect on the pairwise genetic correlations among the four phenotypes: After the pleiotropic effects of T3 concentrations are controlled for, the genetic correlations are reduced by 6% in the case of HDL-C and apo AI and 97% for apo AII and LpAI. Thus, genes that influence T3 have a significant effect on HDL-C, apo AI, apo AII, and LpAI and also on the correlations among these phenotypes.

Adolescent↗
PubMed1992

Husbandry, reproduction and postnatal development of the neotropical muroid rodent Zygodontomys brevicauda.

Laboratory colonies of the Neotropical muroid rodent Zygodontomys brevicauda have been employed in studies of arbovirus epidemiology and are currently the subjects of experimental research on tropical mammalian reproductive physiology and evolutionary quantitative genetics. Captive-bred litters typically consist of 4 or 5 pups weighing 3-4 g each at birth. Adults 20-40 weeks old average 60-80 g with some sexual dimorphism. Females are sexually mature at 3-4 weeks of age, males at 6-8 weeks. Ovulation is spontaneous and gestation is 25 days. Preliminary observations are provided on the microbiological status and parasites of captive-bred animals.

Animal Husbandry↗
PubMed1996

Inheritance of Chediak-Higashi syndrome in Japanese black cattle.

Fifty-six Japanese black cattle affected with Chediak-Higashi syndrome (C-HS) have been referred to Miyazaki University Veterinary Teaching Hospital during the past 12 years, and 44 pedigree records were collected. In pedigree analysis, the parents had no clinical sign, the affected dams had clinically normal calves, and approximately equal numbers of males and females were affected, we therefore considered this syndrome to be an autosomal recessive trait. Quantitative genetic analyses were then made in a restricted area. Segregation analysis by the a priori method in 8 families showed that C-HS was a simple autosomal recessive trait. Furthermore, 36 dams and their 257 offspring (including 8 C-HS affected cattle) were analyzed using population genetics in the same area. The result was the same as in the former analysis.

Animals↗